The present invention relates to the field of engine attachment pylons designed to be interposed between an aircraft wing and an engine, and more particularly to a propulsion assembly comprising such an attachment pylon.
The invention can be used on any type of aircraft equipped for example with jet engines or turboprops.
This type of attachment pylon, also called “EMS” (Engine Mounting Structure), makes it possible, for example, to hang an aircraft engine beneath the wing of the aircraft, or to mount such an engine above the wing.
In general, such an attachment pylon is provided in order to constitute the connection interface between an aircraft engine and the wing of the aircraft. It allows the forces generated by the engine to be transmitted to the structure of the aircraft, and also makes it possible to route fuel, electrical, hydraulic and air systems between the engine and the airframe of the aircraft.
In order to ensure the transmission of forces, the attachment pylon comprises a rigid structure, also called the “primary structure,” which is in general of the “box” type, that is to say formed by an assembly of upper and lower closing spars and of two closing panels or sidewalls. These elements are in general connected to one another via the intermediary of transverse stiffening ribs, when the dimensions of the box justify this.
In addition, the attachment pylon is provided with a mounting system interposed between the engine and the rigid structure of the attachment pylon. This mounting system comprises, overall, at least two engine attachments, generally a forward attachment and an aft attachment.
Moreover, the mounting system comprises in general a device for taking up the thrust forces generated by the engine. In the prior art, this device takes the form, for example, of two lateral struts connected, on one hand, to an aft part of the hub of the intermediate casing arranged in the continuation of the fan casing of the jet engine, or to a forward part of the casing surrounding the core of the jet engine, and, on the other hand, to the aft engine attachment fixed to the casing of the latter.
In the same manner, the attachment pylon also comprises a second mounting system interposed between the rigid structure of this pylon and the wing of the aircraft, this second system habitually consisting of multiple attachments.
Finally, the attachment pylon is provided with a secondary structure which separates and holds the systems while supporting aerodynamic fairings, of which the aft aerodynamic fairing habitually projects rearwards beyond the trailing edge of the wing.
Furthermore, the propulsion assembly is generally equipped with a thermal protection system to protect the box of the rigid structure of the attachment pylon from the heat given off by the engine. Such a thermal protection system comprises a conduit arranged beneath the box to allow a flow of relatively fresh air between the box and the engine, so as to maintain a moderate temperature within the primary structure, in particular with respect to the systems housed within this structure.
However, the arrangement of this conduit beneath the box results in the need to assign a specific volume to the conduit when designing and dimensioning the propulsion assembly. By contrast, it is desirable for aircraft designers to be able to break free from this restriction.
Moreover, such an arrangement of the conduit results in an increase in mass, which is not desirable.
The applicant's international application WO 2007/036521 describes an example of a known type of propulsion assembly, illustrating the problems explained above.